10/08/2010

to figure out how men pick women, scientists have measured every shape and angle of the human face, studied the symmetry of dancers, crafted formulas from the measurements of super models, and had both men and women rank attractiveness based on smelling armpit sweat.

After all this and more, the rules of attraction for the human species are still not understood.

But a short list of scientific rules for the game of love is emerging.

Symmetry equals sex

Good symmetry shows that an individual has the genetic goods to survive development, is healthy, and is a good and fertile choice for mating.

By questioning the study participants, the scientist Thornhill found that men with higher degrees of symmetry enjoy more sexual partners than men of lower symmetry.

Those hips

Body shape is of course important, too. And scientists have some numbers to prove it. Psychologist Devendra Singh of the University of Texas studied people's waist-to-hip ratio.

Women with a WHR of 0.7—indicating a waist significantly narrower than the hips—are most desirable to men.

What exactly is encoded in the hip ratio? A big fat clue to whether the person will have enough energy to care for offspring.

Where fat is deposited on the body is determined by sex hormones; testosterone in men and estrogen in women. If a woman produces the proper amount and mixture of estrogen, then her WHR will naturally fall into the desired range. The same goes for a male's testosterone.

People in the ideal hip-ratio range, regardless of weight, are less susceptible to disease such as cardiovascular disorders, cancer, and diabetes, studies have shown. Women in this range also have less difficulty conceiving.

Face it

The structure of a person's face also gives insight to fertility.

Estrogen caps bone growth in a woman's lower face and chin, making them relatively small and short, as well as the brow, allowing for her eyes to appear prominent, Thornhill explained. Men's faces are shaped by testosterone, which helps develop a larger lower face and jaw and a prominent brow.

Men and women possessing these traits are seen as attractive, Thornhill said, because they advertise reproductive health.

Thornhill also points to the booming nip-‘n'-tuck business—which is very much about improving a person's symmetry—as evidence that people find the quality attractive.

Another recent study revealed that symmetrical dancers are seen as more attractive.

Sniff this

Research reported last month found women both smell and look more attractive to men at certain times of the month.

And symmetrical men smell better.

Borrowing sweaty undershirts from a variety of men, Thornhill offered the shirts to the noses of women, asking for their impressions of the scents. Hands down, the women found the scent of a symmetrical man to be more attractive and desirable, especially if the woman was menstruating.

By now you might be wondering how much of this we're consciously aware of. The rules of attraction, it turns out, seem sometimes to play out in our subconscious.

In some cases, women in Thornhill's study reported not smelling anything on a shirt, yet still said they were attracted to it.

"We think the detection of these types of scent is way outside consciousness," Thornhill said.

A 2002 study found women prefer the scent of men with genes somewhat similar to their own over the scent of nearly genetically identical or totally dissimilar men.

Milos Novotny of the Institute of Pheromone Research at Indiana University has shown that special molecules produced by male mice can simultaneously attract females and repel, and even anger, rival males. Other studies have found similar responses throughout the animal kingdom.

Sex goes visual

Pheromones, like other scents, hitch a ride through the air on other particles, such as water droplets. They generally hover just 10 inches off the ground, however. So odds are slim they'll waft up to a human nose and fuel sudden passion at a nightclub.

Watch any construction worker whistling at a passing woman from half a block away, and you can see how visual cues can be more powerful.

Evolution played a role in this, too.

After our ancestors began to see color, a gene important in the pheromone-signaling pathway suffered a deleterious mutation, making it impossible for the scent signals to reach the brain, Zhang said. Imagine a train, leaving from Los Angeles to New York, discovers that the tracks in St. Louis are destroyed.